Converter valve-pair arrangement

ABSTRACT

Insulative housings are provided for enclosing a plurality of semiconductor rectifiers which form valve-pairs of a pluralbridge-circuit converter. In each of said housings a valve pair of the bridge circuit which is at a higher electrical potential relative to ground is disposed above a valve pair of a bridge circuit which is at a lower electrical potential relative to ground. The housings are spaced sufficiently from one another to provide sufficient insulation between the A-C phases. Further, the space occupied by the lower potential valve pair in a housing serves to insulate the higher potential valve pair therein from ground.

United States Patent [151 3,684,943 Demarest [4 1 Aug. 15, 1972 41CONVERTER VALVE-PAIR FOREIGN PATENTS OR APPLICATIONS A GEMENT 265,3675/1963 Australia ..321/8 C [72] Inventor: Donald M. Demarest,Wallingford,

Pa. Primary Examiner-William H. Beha, Jr. [73] Assignee; GeneralElectric Company Attorney-J. Wesley Haubner et al.

[21] Appl L314 Insulative housings are provided for enclosing aplurality of semiconductor rectifiers which form valve- [52] US. Cl...321/8 C, 317/100, 321/27 R pairs of a pluraI-bridge-circuit converter.In each of [51] Int. Cl. ..H02m 7/00 said housings a valve pair of thebridge circuit which is Field of Search-321m 3 27 R; 1 /2 at a higherelectrical potential relative to ground is 234 H, 100 disposed above avalve pair of a bridge circuit which is at a lower electrical potentialrelative to ground. The [56] References C'ted housings are spacedsufi'iciently from one another to UNITED STATES PATENTS providesufficient insulation between the A-C phases. Further, the spaceoccupied by the lower potential 3,609,510 9/1971 Berkovsky a1 R valvepair in a housing serves to insulate the higher Hesse R potential valvepair therein from ground 3,445,747 5/1969 Laurent ..321/8 C 3,344,3159/1967 Schneider ..317/ 100 5 Claims, 7 Drawing Figures J1 v a}? g 47 W,i 1 d IZ6\ I4' IZZ L r TL ji: 27 *--/4/ IJJA 3;; -35: i 396 I 1 J2-l--;

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ATTORNEY 1 CONVERTER VALVE-PAIR ARRANGEMENT BACKGROUND AND OBJECTS OFTHE INVENTION plural-bridge circuit, high voltage, electric powerconverter.

In the high-voltage electric power conversion art, rectification (i.e.,the conversion of A-C into D-C) or inversion (i.e., the conversion ofD-C into A-C) is ordinarily accomplished by controllable switchingelements or valves. Typically six such valves are interconnected in athree-phase double-way bridge configuration having three A-C terminals,each of which is associated with a separate pair of complementaryvalves, and a set of positive and negative D-C terminals. The two valvesforming each complementary pair, popularly referred to as a valve-pair,are arranged to conduct alternately. By sequentially firing the sixvalves in proper order and in synchronism with the voltages of thethree-phase electric power system to which the A-C terminals of thebridge circuit are connected, the flow of power between the A-C and theD-C terminals can be controlled as desired.

The time in which a valve is fired, measured in electrical degrees fromthe cyclically recurring instant at which its anode voltage firstbecomes positive with respect to the cathode, is known as the firingangle. As the firing angles increase from zero (no phase retard), theaverage magnitude of the rectified voltage between the positive andnegative D-C terminals decreases from its maximum positive level. As thefiring angle approaches 90, the average DC voltage reverses polarity andthe bridge commences to operate in its inverting mode, whereby power canbe transmitted from the D-C to the A-C terminals.

In High Voltage Direct Current (HVDC) systems, converters may consist oftwo three-phase, double-way bridges connected in series between positiveand negative D-C terminals. When arranged in this manner correspondingvalves of the two bridges are fired 30 apart thereby effectuating whatis known in the art as 12- pulse operation. l2-pulse converter'operation eliminates certain system generated harmonics which wouldnaturally arise and flow into the A-C system as a result of theswitching action of the valves. Therefore, when a converter is connectedfor a 12-pulse operation the task of filtering the A-C is madesignificantly easier.

Converter valves comprising high voltage, heavy current, grid controlledmercury arc tubes are well known in the art. More recently solid statevalves comprising switching devices of the multi-layer semiconductortype, e.g., semiconductor controlled rectifiers, have been designed.Such solid state valves commonly utilize a plurality of individualsemiconductor rectifiers connected in parallel arrays for high currenthandling capacity, and a plurality of arrays are connected in series forhigh voltage blocking ability.

It is customary to physically mount one or more of the arrays insuitable heat dissipating pressure assemblies (e.g., see copendingapplication 48AV00273 assigned to the same assignee as my invention) andto support a plurality of electrically interconnected assemblies in acommon enclosure or housing. The walls fo the housing, in particular thebase portions serve as the main support insulation for the valve(s) andare typically made of insulation material. Further, the housing providesthe means through which a cooling fluid may be brought to enable therectifiers therein contained to operate within prescribed, safe temperature ranges. A compact housing having a particularly advantageousconstruction for cooling purposes is disclosed and claimed in copendingapplication 48AV00306, to the same assignee as my invention. As shown inthe latter application the housing is typically disposed inside abuilding, referred to as a valve hall, in which associated coolingequipment (e.g., fans, heat exchangers) is located so that the inside ofthe building, the cooling equipment and the housing form a forcedair-closed loop cooling system.

Irrespective of the type of housing which is used to hold therectifier-mounting assemblies, it should be constructed and arranged toprovide sufiicient insulation between the various conductorsdisposedtherein at different electrical potentials. In very high voltageapparatus comprising a plurality of bridge circuits, there are a numberof possible arrangements which may be utilized for housing solid statevalves. Forexample a separate housing may be provided for all of thesemiconductor rectifiers comprising (1) a single valve; (2) a valvepair, (3) a bridge circuit or (4) the plural bridges making up theentire converter.

Each of the above housing arrangements have several drawbacks when usedin very high-voltage, plural-bridge converters. This can be appreciatedby considering the use of such arrangements in a l2-pulse" convertercomprising a pair of serially connected threephase double way bridges.

Insofar as the first mentioned arrangement (hereinafter referred to asthe single-valve-housing) is concerned, the converter requires the useof 12 separate housings (i.e., one for each valve). Further, thehousings enclosing valves whose potentials are above or below groundpotential have to be disposed upon insulative bases to properly insulatethem from ground. In view of these factors, the single-valve-housingarrangement may necessitate the provision of a relatively large space inthe valve hall.

Insofar as the second arrangement (hereinafter referred to as thevalve-pair-housing") is concerned, although only six of such housingswould be required (i.e., one for each valve pair), still the housingsenclosing valve pairs which are at potentials above or below groundpotential have to be disposed upon insulative bases to insulate themfrom ground. Therefore, the valve-pair-housing arrangement, like thesingle-valve arrangement, may occupy an undesirably large space in thevalve hall.

Insofar as the third arrangement (hereinafter referred to as thebridge-housing) is concerned, although only two such housings would berequired (i.e., one for each bridge circuit), nevertheless each would berelatively large in order to provide the necessary insulation betweenthe A-C phase conductors contained therein. Large housings arerelatively expensive to construct, and access to the semiconductordevices mounted therein may be more difficult than with compacthousings. Further, the housing enclosing the valves of the bridge whichis at the highest potential (plus or minus) relative to ground potentialrequires a relatively large insulative base in order to properlyinsulate them from ground.

Insofar as the fourth arrangement (hereinafter referred to as the"plural-bridge-housing) is concerned, only one housing is required sinceall of the converter valves are disposed therein. However such a housingis necessarily large and expensive to construct. Further, individualassembly accessibility is rendered that much more difficult owing to thelarge housing size.

It is therefore a general object of my invention to provide a housingarrangement for selected solid-state valves of electric power conversionapparatus which overcomes the disadvantages of the prior art.

It is a further object of my invention to provide relatively compacthousings for preselected electric valves of a high voltage converter tominimize the amount of space required for the apparatus while providingnecessary insulation for the various conductors and live circuitelements disposed therein.

SUMMARY OF THE INVENTION In accordance with one form of my inventionseparate insulative housings are provided for enclosing a plurality ofrectifier-holding assemblies which form valve-pairs of aplural-bridge-circuit converter apparatus. One valve-pair of each of theconverters plural bridge circuits is disposed within a single housing.They are arranged such that the valve pair of the bridge circuit whichis at a higher electrical potential relative to ground is disposed abovea valve-pair of a bridge circuit which is at a lower electricalpotential relative to ground. With this arrangement, the space betweenseparate housings is advantageously used for the necessary insulationbetween the A-C phases (.e., line-to-line insulation), while the spaceoccupied in each housing by the lower potential valve-pair is utilizedto insulate the higher potential valve-pair from ground. Accordingly,the total space within a valve hall which is provided for disposition ofa high voltage converter of a given rating utilizing my housingarrangement is less than with prior art housing arrangements.

BRIEF DESCRIPTION OF THE DRAWINGS My invention will be better understoodand its various objects and advantages will be more fully appreciatedfrom the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a schematic one line diagram of a typical I-IVDC system inwhich my invention can be ad vantageously used.

FIG. 2 is a schematic circuit of one pole of the North converter shownin FIG. 1.

FIG. 3 is a simplified schematic diagram of a typical valve in theconverter shown in FIG. 2.

FIG. 4 is a perspective view of a panel for mounting a plurality ofrectifier-holding, heat-dissipating assemblies in a unitary housing.

FIG. 5 is a front view, partially in section, of a housing for selectedvalves of the converter with a schematic diagram of those valves, inphantom lines, superimposed thereon to depict the physical arrangementof the valves therein.

FIG. 6 is a perspective view of a portion of the housing shown in FIG.5.

FIG. 7 is a front view in section of a valve hall in which my housingsand associated cooling equipment is disposed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Some of the featuresshown and described herein form the subject matters of copending patentapplications (48AV00273 and 48AVOO306 assigned to the same assignee asmy invention.

FIG. I of the present application is a one-line representation of asource 1 (AC Gen.) supplying electricity to a load 2 (A-C Load) via aD-C system comprising a pair of high voltage converter plants 3interconnected by a DC link 4. The link comprises a nominally positiveD-C conductor 5 paralleled by a relatively negative D-C conductor 6,each conductor may have smoothing chokes or reactors 7 in seriestherewith. The converter at the source terminal of the transmission lineis called North Converter (rectifying)" Its A-C side is coupled to thesource 1 bymeans of a circuit breaker 8, and the A-C system impedance issymbolically shown at 9. The converter at the opposite terminal of thetransmission line is called South Converter (inverting), and its A-Cside is coupled to the load 2 by way of another circuit breaker l0 andA-C cystem impedance 11. g

In practice the electric power system shown in FIG. 1 could bebidirectional. For example, an additional source of power could becoupled to the A-C network fed by the South converter for supplying, ondemand, other loads coupled to the AC side of the North converter. Thedirection of power in the D-C transmission line is readily reversed bychanging the operating modes of the converters at the respectiveterminals so that the South one acts as a rectifier and the North oneacts as an inverter.

FIG. 2 is a schematic circuit diagram of one pole of the North converter3 of the FIG. 1 system. It will be observed that this pole comprisesfirst and second power transformers l2 and 13 in combination with firstand second A-C/D-C bridges 14 and 15, respectively. The firsttransformer 12 has two inductively coupled sets 16 and 17, of threestar-connected windings. The windings of one set 16 are connectedrespectively to three separate terminals A, B, and C which are adaptedto be connected to the respective phases of a threephase A-C electricpower system whose phase rotation is A, B, C. The windings of thecompanion set 17 are respectively connected to A-C terminals 0, b, and cof the first bridge 14. The bridge 14 has a pair of DC terminals d ande, with the former being connected to the positive D-C terminal of theillustrated converter.

The second transformer 13 of the shown pole of the North convertercomprises a set 18 of three wye connected windings inductively coupledto a set 19 of three delta connected windings. The windings of the set18 are respectively connected to the three terminals A, B, and C, whilethe windings of the companion set 19 are respectively connected to theA-C terminals a, b and c of the second bridge 15. With this arrangement,the AC voltages at the latter terminals will lag those at thecorresponding terminals a, b, and c of the first bridge 14 by a phaseangle of 30 electrical degrees. It should be noted that a singletransformer three phase or one phase having two secondaries (one deltaconnected and one Wye connected) may be utilized in lieu of thetransformers 12 and 13 shown. The bridge has a pair of D-C terminals dand e, the former being connected to terminal e of bridge 14, the latterbeing connected to ground. Thus the two bridges 14 and 15 are connectedin series with one another between the positive and ground terminals ofthe illustrated converter pole, and the DC voltage across theseterminals is the sum of the outputs of the respective bridges.

Bridge 14 comprises six identical controlled valves 141, 142, 143, 144,145 and 146 arranged in a threephase double-way bridge configuration.Thus, the cathodes of the odd-numbered valves are connected in common tothe upper D-C terminal d of the bridge, and the anodes of theeven-numbered valves are connected in common to the other D-C terminale. The anode of the valve 141 and the cathode of valve 144 are bothconnected to the first terminal-a of the three-phase A-C terminals ofthe bridge. Valves 141 and 144 thus form the valve-pair associated withphase A. The anode of valve 143 and the cathode of valve 146 are bothcon nected to the second A-C terminal b. Valves 143 and 146 thus formthe valve-pair associated with phase B. The anode of valve 145 and thecathode of valve 142 are both connected to the third A-C terminal 0.Valves 145 and 142 thus form the valve-pair associated with phase C. Byfiring these six valves in their numbered sequence at intervals of 60electrical degrees, threephase electric power supplied to the A-Cterminals of the bridge can be converted to D-C power.

Bridge 15 is composed of valves 141', 142, 143, 144', 145', and 146whose arrangement and operation are similar to the valves of bridge 14.The gate pulses for sequentially firing the valves of bridge 15 will beinterleaved with the gate pulses for the correspondingly numbered valvesin the leading bridge 14, thereby forming a l2-pulse converter.

The average magnitude of the rectified voltage between the DC terminalsd and e is maximum when the firing angle of these gate pulses is zero.By increasing the firing angle to nearly 90, the DC voltage can bereduced to zero. Still greater firing angles are used when the bridge isoperating in its inverting mode. When operating in this mode the D-Celectric power supplied to terminals d and e is converted by the bridgeto three-phase A-C power.

The DC voltage rating of either bridge depends on the individual voltagerating of each valve. FIG. 3 is a simplified diagram of valve 141. Thisvalve, like all the others, comprises a plurality of semiconductorrectifier devices 20. The rectifiers are connected in parallel arraysfor high current handling capacity, and a plurality of these arrays areconnected in series to raise the blocking voltage rating of the valve.Although rectifiers 20 are shown schematically as thyristors (i.e.,controlled rectifiers) it should be apparent that other rectifier types(e.g., diodes) may be used, depending upon the function to be performed.In a I-IVDC system each converter valve 141, 142, 143, 144, 141', 142',143', 144 may include, as shown in FIG. 5, a series string of 16 arraysof four parallel thyristors each.

In FIG. 4 of copending application 48AV00273 there is shown aheat-dissipating, rectifier-holding assembly for mounting two thyristorsin series in each of four parallel paths. A plurality of such assembliesmay be mounted on boards of panel structures and electricallyinterconnected to form a converter valve like that discussed above. InFIG. 4 there is shown a panel board 21 which is adapted to be disposedalong with like panel boards in a housing arranged in accordance with myinvention. Mounted upon panel board 21 are a pair ofheat-dissipating-rectifier holding assemblies 22. Although theseassemblies can take other suitable forms, they are particularly shown asbeing the same as that shown in FIG. 4 of the first mentioned co-pendingapplication. Each assembly includes plural heat dissipating electrodes23 which electrically contact respective terminals of the rectifiers 20to apply pressure to them and to extract the heat which they generate inoperation. To the latter end a plurality of narrow cooling fluid ducts24 are provided in the electrodes 23. These ducts are formed by aplurality of heat dissipating fins 25 and are disposed immediatelyadjacent the rectifiers. The ducts are narrow so that upon the passageof a high velocity cooling fluid therethrough, turbulence results whicheffectuates efficient heat extraction.

Each of the assemblies 22 are directly mounted on panel boards 21 sothat the cooling ducts 24 in electrodes 23 communicate with apertures 26in the panel boards. These apertures can be seen in FIG. 5. Panel board21 also serves to mount voltage control and gate pulse forming circuitry27 for the rectifiers and a saturable core reactor 28 connected inseries with the rectifiers as well as protective circuitry (not shown)for the rectifiers. More information about the details and operation ofsome of these circuits canbe found in U.S. Pat. No. 3,424,664 (Dewey).Panel board 21 is made of an electrical insulating material to preventthe rectifiers from being short-circuited since electrodes 23 aremounted directly to the panel board. Suitable means (not shown) areprovided for interconnecting the assemblies on the panel boards so thatthe rectifier arrays are connected in series between terminals (notshown) at opposite ends of each panel board. FIG. 5 is a front view,partially broken away, of a valve housing 29 arranged in accordance withmy invention. Housing 29 comprises a pair of insulative sidewalls (onlyone of which, 30, can be seen) a pair of insulative ends walls 32 and33, and insulative top wall 34, and an insulative bottom wall 34a.Disposed inside the housing are a plurality of panel boards 21 like thatshown in FIG. 4. Each panel board is adapted for easy removal from thehousing. Toward that end the housing may include openings in thesidewalls through which the panels may be passed for insertion in orremoval from the housing. To expedite their insertion or removal, thepanels may be adapted for sliding on tracks provided in the housingnormal to the sidewalls. Cover plates may be provided for closing thesidewall openings.

As can be seen from FIG. 5 the panel boards are disposed in pairs whichare parallel to and closely spaced apart from each other so that theirapertures 26 are aligned. Each pair forms a separate panel structure.Pair 35a and 35b form structure 35. Pair 36a and 36b form structure 36.Pair 37a and 3712 form structure 37. Pair 38a and 38b form structure 38.Pair 39a and 39b fonn structure 39. Pair 40a and 40b form structure 40.

Pair 41a and 41b form structure 41. Pair 42a and 42b form structure 42.Although the panel structures are shown as including two panel boards21, panel structures including more or less than two panel boards canalso be utilized.

As can be seen from FIG. 5, an insulating member 43 is connected betweenpanel structures 35 and 36, an insulating member 44 is connected betweenpanel structures 36 and 37, and an insulating member 45 is connectedbetween panel structures 37 and 38. Panel structures 35, 36, 37, and 38and members 43, 44 and 45, as a group, form a wall of a pair of ducts 46and 47. An insulating member 48 is connected between panel structures 39and 40, an insulating member 49 is connected between panel structures 40and 41 and an insulating member 50 is connected between panel structures41 and 42. Panel structures 39, 40, 41 and 42 and members 48, 49 and 50,as a group, form another wall of duct 47 and a wall of another duct 51.i

The function of duct 47, hereinafter called the inlet duct, is to carrya cooling fluid to the panel structures in the housing so that it canextract the rectifiergenerated heat from the panel-mounted-assemblies.The function of ducts 46 and 51, hereinafter called the outlet ducts, isto provide a passage through which the fluid can pass after havingextracted the rectifier generated heat.

The top wall 34 of housing 29 includes an aperture 52 which communicateswith duct 47. This aperture is provided to permit the ingress of thecooling fluid into the inlet duct and is denoted as an entranceaperture. The bottom wall 34a of the housing includes two apertures 53and 54. Aperture 53 communicates with duct 46 and aperture 64communicates with duct 51. These apertures are provided to permit thefluid to exit the housing and are denoted as exit apertures.

The path of fluid flow through the housing is as follows: the fluidenters housing 29 through entrance aperture 52 into inlet ducts 47. Itflows through this duct to the panel structures forming the wallsthereof and from there it passes through panel apertures 26 and entersthe narrow cooling ducts 24 of the panel mounted assemblies 22. In itspassage through these ducts it extracts the rectifier-generated heat sothat its temperature is necessarily increased. Upon exiting ducts 24 theelevated temperature fluid passes through respective outlet ducts 46 and51 and corresponding exit apertures 53 and 54 to exit the housing.decrease Preferably, as is shown in FIG. 5, the parallel panelstructures are laterally offset from one another so that the inlet ductsdecrease in cross sectional area in the direction of the fluid flowwhile the outlet ducts increase in cross sectional area in thatdirection. For example, panel structure 36 is parallel to and laterallyoffset from panel structure 35, panel structure 37 is parallel to andlaterally offset from panel structure 36 and panel structure 38 isparallel to and laterally offset from panel structure 37. Similarly,panel structure 40 is parallel to and laterally offset from panelstructure 39, panel structure 41 is parallel to and laterally offsetfrom panel structure 40 and panel structure 42 is parallel to andlaterally offset from panel structure 41. When arranged in this mannerthe cross sectional area of the portion 55 of inlet duct 47 locatedbetween panel structures 35 and 39 is larger than the cross sectionalarea of the duct portion 56 located between panel structures 36 and 40,which in turn is larger than the cross sec tional area of the ductportion 57 located between panel structures 37 and 41, which in turn islarger than the cross sectional area of the duct portion 58 locatedbetween panel structures 38 and 42. Further, the cross sectional area ofthe portion 59 of outlet duct 46 located between side wall 32 and panelstructure 35 is smaller than the cross sectional area of duct portion 60located between the sidewall and panel structure 36 which in turn issmaller than the cross sectional area of duct portion 61 located betweenthe sidewall and panel structure 37, which in turn is smaller than thecross sectional area of the duct portion 62 locate between the sidewalland panel structure 38.

If the pressure drop along each path that the cooling fluid takesthrough the housing is approximately equal, the amount of fluid flowingin each path will also be approximately equal and each rectifier willreceive a substantially equal share of thecooling fluid. Assemblies 22are constructed to such close tolerances that the pressure drop throughthe ducts 24 in any one of them at any given fluid flow will be the sameas the pressure drop through the ducts of another. The cross sectionalarea of respective inlet and outlet duct portions are configured inaccordance with the teachings in copending application 48AV00306 so thatpressure drop in each duct portion is approximately equal. Therefore,the total pressure drop along each path is approximately equal, andefficient cooling of all the rectitiers is obtained.

The insulating base and walls and the various internal supportingmembers and barriers of the valve housing 29 are properly selected anddimensioned to provide adequate electrical insulation between the manyrectifier-holding-assemblies and interconnecting conductors which aredisposed therein. In accordance with my invention, as shown in FIG. 5,the space required for the requisite insulation is most efficientlyutilized, and the net space which must be provided in the valve hall isconsequently minimized, by locating in a single housing 29 all of thepaneLmounted assemblies forming two valve-pairs which are respectivelyassociated with adjoining bridge circuits of the converter. Three ofthese housings are therefore required for the illustrated 12- pulseconverter. The housing is arranged with the valve pair (141, 144) of thebridge circuit 14 which is at a higher electrical potential relative toground disposed above the valve pair (141', 144') of the lower potentialbridge 15. In arranging each of the three housings in this manner, Iutilize the space occupied by the lowerpotential valve-pair to insulatethe rectifier-holding-assemblies and conductors forming thehigher-potential valve-pair from the closest ground plane which is theground upon which the housing is disposed. The space separating theindividual housings is utilized to insulate the A-C terminals of eachbridge from one another, thereby ensuring sufficient insulation againstthe relatively large phase-to-phase voltages which exist between theseterminals in a high-voltage converter.

The serial connection of any valve pair of one bridge circuit and anyvalve pair from another lower voltage bridge'circuit forms what can bedenominated as a quadri-valve." As shown in FIG. 5 a quadri-valve madeup of valve-pairs 141, 144 and 141', 144' is disposed in housing 29.Another housing 29' may be used for enclosing and supporting aquadri-valve" made up of valve-pairs 143, 146 and 143', 146' and a thirdhousing 29 may be used for a quadri-valve made up of valve-pairs 145,142 and 145, 142. A converter construction using such an arrangementfulfills the design objective of minimizing the amount of space whichmust be provided in the valve hall for a converter of a given rating.

As is indicated by the phantom lines in FIG. 5, the rectifiers in theassemblies mounted on panel structures 35 and 39 of the housing 29 formvalve 141, the rectifiers in the assemblies mounted on panel structures36 and 40 form valve 144, the rectifiers in the assemblies mounted onpanel structures 37 and 41 form valve 141' and the rectifiers in theassemblies mounted on panel structures 38 and 42 form valve 144'. Thephysical disposition of the electrical connectors used to interconnectthe panel structures in accordance with the phantom schematic of FIG.can be seen in FIG. 6.

FIG. 6 shows, in perspective, the upper half of housing 29 and thebuswork which electrically interconnects the panel structures thereincontained. As can be 'seen, a conductor or bus bar 63 is providedoutside the front wall 30 of the housing 29. This bus bar provides theDC terminal d for the quadri-valve shown. A bus bar 64 is providedoutside the back wall of the housing to interconnect panel boards 39aand 39b. A bus bar 65 disposed outside of the front wall to interconnectpanel 39b and 35a, a bus bar 66 is provided outside the backwall tointerconnect panel 35a and 35b, and a bus bar 67 is provided outside thefrontwall to provide the phase A connection (A-C terminal a of bridge14) and to connect panel 35a and panel 361;. A bus bar 68 is providedoutside the backwall to interconnect panels 36b and 36a, a bus bar 69 isprovided outside the frontwall to interconnect panel 36a with panel 40b,a bus bar 70 is provided outside the backwall to interconnect panel 40band 40a, and a bus bar 71 is provided outside the frontwall to providethe common D-C connection (terminals e and d) between bridges 14 and andto connect panel 40a to panel 410. Similar bus bars (not shown) are usedto interconnect the remaining panels forming the quadri-valve.

Of the two bridges forming the pole of the converter shown, bridge 14 isat a higher potential relative to ground than bridge 15. Accordingly,more insulation must be provided between valve pair 141, 144 and groundthan between valve-pair 141', 144' and ground. The insulation for thelatter valve pair may consist of a block of insulating material 72 uponwhich the housing 29 is disposed. The height of block 72 is a functionof the phase A line-to-ground voltage. The insulation between the formervalve pair and the ground is supplied by the space in which valve pair141, 144' is disposed. Thus the space in which valve pair 141, 144' islocated not only serves to house that valve pair but also serves toprovide the necessary insulation between valve pair 141, 144 and ground.

Insofar as the voltage between the A-C terminals of any of theconverters bridge circuits is concerned, the housings 29, 29 and 29" aredisposed sufficiently far apart so that the space therebetween serves asthe necessary line insulation. Insulation for the line-to-line voltagebetween the two A-C terminals associated with ill the valve-pairs makingup the quadri-valve" (e.g., terminals a and a) is provided by making thedimensions of each housing such that phase conductors associated withthose phases are spaced sufficiently apart from each other to precludearcing. Normally the height of housing which is necessary to providesufficient insulation between the DC. terminal d and ground will providesufficient insulation to support the line-to-line voltage of the two A-Cterminals of the quadri-valve.

It should be noted at this point that while I have shown onequadri-valve as including valve pairs 141, 144 and 141', 144, it shouldbe apparent that either valve pair 143', 146 or 145, 142 can be used inlieu of valve pair 141, 144 to form the quadri-valve." The valve pairarrangement shown however is preferable in that it maintains properphase rotation and simplifies connections between the rectifier holdingassemblies forming the two valve-pairs which are enclosed in the samehousing.

It should also be noted that if the converter consists of more than twobridge circuits then more than two valve pairs can be disposed withineach housing. For example, if the converter has four bridges (for 24pulse operation) a valve pair from each of the four bridges could bedisposed in a single housing with the valve pair at the highestelectrical potential disposed above the valve pair at the next highestpotential and so on.

FIG. 6 shows a building or valve hall 73 in which the quadri-valvehousings 29, 29, and 29" may be disposed. The cooling system showntherein is of the two plenum, closed-loop, forced air type. As can beseen, building 73 includes a grounded floor or base 74, upon whichhousings 29, 29' and 29" are disposed. Each housing is insulated fromground by insulating block 72. The air space 75 above the building flooracts as one plenum while the enclosed spaces 76 below the floor act assecond plenums. The first plenum communicates with the inlet ductsinside the housings via their entrance apertures. The second plenumscommunicate with the outlet ducts inside the housings via their exitapertures.

A plurality of fans 77 are associated with each plenum 76 (although onlyone of which can be seen) and are disposed below the floor 74. Thesefans communicate with their associated plenums 76 to draw the air fromthe upper plenum 75 through the respective housing ducts and the heatdissipating assemblies into the lower plenums 76. From these lowerplenums the air, which was heated in extracting heat from therectifiers, is forced through an air-to-glycol heat exchangers 78whereupon the temperature of the air is reduced to a predeterminedtemperature (depending upon the amount of rectifier-heat to beextracted). The cooled air is then returned to the upper plenum viaapertures 79 in floor 74. It should be noted that in lieu of separateplenums 76 associated with each of the quadri-valve housings a commonlower plenum may be utilized. A plurality of fans and heat exchangersmay be utilized in conjunction with the common lower plenum of such anarrangement.

The upper plenum, being the interior of building 73, is large enough tobe considered as an infinite air source. Thus air turbulence is minimalat the housing entrance apertures so that each housing inlet ductreceives the same amount of air as any other inlet duct.

Similarly, the lower plenums 76 are made large enough so that airturbulence therein is minimized whereupon each fan can act upon an equalamount of air with no one fan working harder or easier than others.

While I have shown my quadri-valves in a converter utilizing twoserially connected AC/DC bridges per pole, it should be apparent that myhousing arrangement can be used for any converter utilizing plural AC/DCbridges connected between a DC terminal and ground.

Accordingly, while I have shown and described a particular embodiment ofmy invention, it will be obvious to those skilled in the art thatvarious changes and modifications may be made without departing from myinvention in its broader aspects; and I, therefore, intend herein tocover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a high voltage electric power converter including a plurality ofhigh current electric valves interconnected to form first and secondbridge circuits, said first bridge circuit being at a higher electricalpotential relative to ground than said second bridge circuit, each ofsaid bridge circuits comprising at least two valvepairs, the improvementcomprising: a first electrically insulative housing disposed upon agrounded base, said first housing enclosing a first one of thevalve-pairs of said first bridge circuit and a first one of thevalve-pairs of said second bridge circuit, said valve-pairs beingarranged therein with the latter valve-pair physically interposedbetween the former valve-pair and the grounded base, and a secondelectrically insulative housing spaced apart from said first housing anddisposed upon said base, said second housing enclosing a second one ofthe valve-pairs of said first bridge circuit and a second one of thevalve-pajrs of said second bridge circuit, said valve-pairs beingarranged with the latter valve-pair physically interposed between theformer valve-pair and the grounded base, whereby the higher potentialvalve-pairs in each of the housings are insulated from the grounded baseby the housing space occupied by the lower potential valve-pair.

2. The converter as specified in claim 1 wherein electrically insulativemembers are provided upon which said housings are disposed to insulatesaid housings from said grounded base.

3. The converter as specified in claim 1 wherein each of said valvescomprises a plurality of electrically interconnected semiconductorrectifier devices.

4. In a high voltage electrical converter apparatus including aplurality of high current rectifier valves connected to form first andsecond three-phase doubleway bridge circuits each having first, secondand third valve-pairs whose respective A-C terminals are adapted to beconnected to the different phases of a three-phase alternating voltagesystem, said first bridge circuit being at a higher electrical potentialrelative to ground than said second bridge circuit, the improvementcomprising: a first electrically insulating housing, disposed upon agrounded base and enclosing a first valve-pairs of the respective firstand second bridge circuits, with the first valve-pair of second bridgecircuit being physically interposed between the first valve-pair of thefirst bridge circut and said grounded ase; a second ou ing, ispose uponsaid grounded ase and space su ficiently from said first housing toprovide insulation for the higher phase-to-phase voltage between saidA-C terminals, said second housing enclosing the second valve-pairs ofthe respective first and second bridge circuits with a second valve-pairof the second bridge circuit being physically interposed between thesecond valve-pair of the first bridge circuit and said grounded base;and a third housing, disposed upon said grounded base and spacedsuificiently from said first and second housings to provide insulationfor the highest phase-tophase voltage between said A-C terminals, saidthird housing enclosing the third valve-pairs of the respective firstand second bridge circuits with the third valve-pair of the secondbridge circuit being physically interposed between the third valve-pairof the first bridge circuit.

5. The converter apparatus as specified in claim 4 wherein said valvescomprise a plurality of interconnected semiconductor rectifier devices.

1. In a high voltage electric power converter including a plurality ofhigh current electric valves interconnected to form first and secondbridge circuits, said first bridge circuit being at a higher electricalpotential relative to ground than said second bridge circuit, each ofsaid bridge circuits comprising at least two valve-pairs, theimprovement comprising: a first electrically insulative housing disposedupon a grounded base, said first housing enclosing a first one of thevalve-pairs of said first bridge circuit and a first one of thevalve-pairs of said second bridge circuit, said valve-pairs beingarranged therein with the latter valve-pair physically interposedbetween the former valve-pair and the grounded base, and a secondelectrically insulative housing spaced apart from said first housing anddisposed upon said base, said second housing enclosing a second one ofthe valve-pairs of said first bridge circuit and a second one of thevalve-pairs of said second bridge circuit, said valve-pairs beingarranged with the latter valvepair physically interposed between theformer valve-pair and the grounded base, whereby the higher potentialvalve-pairs in each of the housings are insulated from the grounded baseby the housing space occupied by the lower potential valve-pair.
 2. Theconverter as specified in claim 1 wherein electrically insulativemembers are provided upon which said housings are disposed to insulatesaid housings from said grounded base.
 3. The converter as specified inclaim 1 wherein each of said valves comprises a plurality ofelectrically interconnected semiconductor rectifier devices.
 4. In ahigh voltage electrical converter apparatus including a plurality ofhigh current rectifier valves connected to form first and secondthree-phase double-way bridge circuits each having first, second andthird valve-pairs whose respective A-C terminals are adapted to beconnected to the different phases of a three-phase alternating voltagesystem, said first bridge circuit being at a higher electrical potentialrelative to ground than said second bridge circuit, the improvementcomprising: a first electrically insulating housing, disposed upon agrounded base and enclosing a first valve-pairs of the respective firstand second bridge circuits, with the first valve-pair of second bridgecircuit being physically interposed between the first valve-pair of thefirst bridge circuit and said grounded base; a second housing, disposedupon said grounded base and spaced sufficiently from said first housingto provide insulation for the higher phase-to-phase voltage between saidA-C terminals, said second housing enclosing the second valve-pairs ofthe respective first and second bridge circuits with a second valve-pairof the second bridge circuit being physically interposed between thesecond valve-pair of the first bridge circuit and said grounded base;and a third housing, disposed upon said grounded base and spacedsufficiently from said first and second housings to provide insulationfor the highest phasE-to-phase voltage between said A-C terminals, saidthird housing enclosing the third valve-pairs of the respective firstand second bridge circuits with the third valve-pair of the secondbridge circuit being physically interposed between the third valve-pairof the first bridge circuit.
 5. The converter apparatus as specified inclaim 4 wherein said valves comprise a plurality of interconnectedsemiconductor rectifier devices.